1. Technical Field
The present invention relates to wireless communication, and more specifically, to a method of transmitting data in a multiple antenna system.
2. Related Art
Wireless communication systems are widely used to provide various types of communications. For example, voices and/or data are provided by the wireless communication systems. General wireless communication systems provide multiple users with one or more shared resources. For example, the wireless communication systems may use a variety of multiple access techniques such as code division multiple access (CDMA), time division multiple access (TDMA), and frequency division multiple access (FDMA).
Orthogonal frequency division multiplexing (OFDM) uses a plurality of orthogonal subcarriers. OFDM uses the characteristic of orthogonality between Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT). A transmitter transmits data after performing IFFT on the data. A receiver restores original data by performing FFT on a received signal. The transmitter uses IFFT to combine multiple subcarriers, and the receiver uses corresponding FFT to separate the multiple subcarriers. According to OFDM, complexity of the receiver may be lowered in a frequency selective fading environment of wideband channels, and spectral efficiency may be enhanced through selective scheduling or the like in a frequency domain by utilizing different channel characteristics of subcarriers. Orthogonal frequency division multiple access (OFDMA) is a multiple access scheme based on OFDM. According to OFDMA, efficiency of radio resources may be enhanced by assigning different subcarriers to multiple users.
Recently, multiple input multiple output (MIMO) systems are spotlighted in order to maximize performance and communication capacity of wireless communication systems. The MIMO technique is a method that can improve transmission efficiency of transmit and receive data by employing multiple transmit antennas and multiple receive antennas, getting out of using one transmit antenna and one receive antenna used up to the present. The MIMO system is also referred to as a multiple antenna system. The MIMO technique does not depend on a single antenna path in order to receive one whole message, but applies a technique that gathers fragmented data segments received through a plurality of antennas and completes a message. As a result, data rate may be improved within a specific range, or a system range may be increased for a specific data rate.
Hereinafter, downlink means transmission from a base station to a user equipment, and uplink means transmission from the user equipment to the base station.
Generally, the base station schedules radio resources of uplink and downlink in a wireless communication system. User data or control signals are carried on the uplink radio resources and downlink radio resources. A channel carrying user data is referred to as a data channel, and a channel carrying control signals is referred to as a control channel. The control signals include various types of control signals needed for communications between the base station and the user equipment. For example, control signals needed for scheduling radio resources in a multiple antenna system include channel quality indicator (CQI), rank indicator (RI), precoding matrix indicator (PMI), and the like. The user equipment transmits uplink control signals such as CQI, RI, PMI and the like to the base station, and the base station schedules radio resources for uplink and downlink based on the control signals received from a plurality of user equipments. The base station informs the user equipment of RI, PMI, modulation and coding scheme (MCS) of the scheduled radio resources through the downlink control signals.
Errors may occur in uplink control signals transmitted from the user equipment to the base station in the process of transmission. If an error occurs in an uplink control signal, it may cause difficulties to schedule radio resources. However, it is not clearly suggested how to make up for an error when the error occurs in the uplink control signal that is needed by the base station for scheduling radio resources.
Therefore, there is a need for a method of preparing for errors that occur in uplink control signals.